A flange gasket is the core sealing component between two flanges, which generates compression rebound through bolt compression, fills the micro gaps of the flange sealing surface, and prevents gas and liquid medium leakage. It is widely used in pipeline, pressure vessel, and valve flange connections. The selection of the core depends on the four elements of temperature, pressure, medium, and flange sealing surface form.
1, Core classification of gaskets (3 major categories, including materials, parameters, and applicable working conditions)
(1) Non metallic soft pad (low pressure, room temperature, weak corrosion, mainly PN ≤ 1.6MPa)
Overall soft, easy to compress, low cost, average rebound, not resistant to high pressure and high temperature, must be replaced every time disassembled.
Rubber gasket (NBR nitrile, EPDM EPDM, FKM fluororubber)
Temperature resistance: -40~120 ℃ (fluorine glue -20~200 ℃); Pressure resistance: ≤ 1.6MPa
Usage: Water, air, regular oil, drinking water; EPDM is resistant to water and steam, NBR is resistant to oil, and fluorine rubber is resistant to strong corrosion
Disadvantages: prone to aging and carbonization above 200 ℃, not resistant to high temperature and high pressure
Non asbestos fiber gasket (non asbestos gasket)
Temperature resistance: -50~300 ℃; Pressure resistance: ≤ 4.0MPa
Usage: Steam, hot oil, water, common acid and alkali, replacing traditional asbestos gaskets, suitable for chemical/HVAC applications
Polytetrafluoroethylene (PTFE/PTFE) gasket
Temperature resistance: -200~260 ℃; Pressure resistance: ≤ 2.5MPa
Advantages: Extremely strong acid and alkali resistance, solvent resistance, clean and precipitation free, specialized for pharmaceuticals, food, and strong corrosive media
Disadvantages: High temperature is prone to cold flow creep, and should be used with caution in situations with alternating pressure
Flexible graphite flat gasket
Temperature resistance: -200~600 ℃ (aerobic environment ≤ 450 ℃); Pressure resistance: ≤ 6.4MPa
Advantages: High temperature resistance, good thermal conductivity, strong rebound, suitable for medium and high temperature steam and hot oil
(2) Half metal gasket (most commonly used! Suitable for medium temperature and medium pressure, balancing strength and elasticity)
Metal+non-metal composite, excellent rebound, temperature and pressure resistance, suitable for most industrial working conditions.
Metal wound gasket (spiral wound gasket, national standard GB4622)
Structure: V/W-shaped metal steel strip+flexible graphite/PTFE strip alternately wound, can add inner and outer rings
Metal material: 304/316L stainless steel, carbon steel; Filling: Graphite (high temperature), PTFE (corrosive)
Temperature resistance: -200~550 ℃; Pressure resistance: ≤ 25MPa
4 types:
Basic type: tenon groove surface, concave convex surface flange
Inner ring: RF protrusion, anti medium erosion, positioning
With outer ring: FF plane, precise positioning, most commonly used
Inner and outer rings: high pressure, high temperature, flammable and explosive media
Usage: Petroleum, chemical, power, steam pipelines, universal gaskets
Metal coated gasket (ladle gasket)
Structure: Thin metal shell (304/316) wrapped around graphite/asbestos core
Temperature resistance: -200~500 ℃; Pressure resistance: ≤ 10MPa
Usage: Heat exchanger, atmospheric pressure vessel, medium pressure pipeline
(3) All metal gasket (high pressure, high temperature, extreme working conditions, PN ≥ 10MPa)
Pure metal processing, high hardness, extremely strong temperature and pressure resistance, requiring high flange surface accuracy and large bolt pre tightening force.
Metal toothed gasket (toothed gasket)
Material: 304, 316L, Monel alloy
Temperature resistance: -200~800 ℃; Pressure resistance: ≤ 40MPa
Features: serrated surface, embedded into flange surface after compression, extremely strong sealing, high-pressure heat exchanger, boiler flange
Metal ring gasket (octagonal gasket, elliptical gasket, dedicated for RJ ring connection surface)
Material: Carbon steel, 304, 316, Hastelloy
Temperature resistance: -200~800 ℃; Pressure resistance: ≤ 100MPa
Usage: High pressure hydrogenation, nuclear power, refining equipment, only compatible with RJ ring connection flange
2, Match the flange sealing surface with the gasket (key! Mismatching will result in leakage)
FF full flat flange: non-metallic flat gasket, with inner and outer wrapped gaskets
RF flange (most commonly used): with inner ring wrapped gasket, graphite gasket, non asbestos gasket
MFM Concave Convex Flanges: Basic types of winding pads, graphite pads
TG tenon groove flange: basic winding gasket, PTFE gasket (anti extrusion gasket)
RJ ring connection flange: only use octagonal gasket/elliptical gasket (metal ring gasket)
3, Gasket selection mnemonic (quick selection)
Low pressure room temperature water oil → Non asbestos/rubber flat pad
Medium temperature and medium pressure universal → Metal wound gasket (with inner and outer rings)
Strong corrosive acid and alkali → PTFE pad, PTFE winding pad
High temperature steam hot oil → flexible graphite pad, graphite winding pad
High pressure, high temperature, highly toxic → Metal toothed pads, octagonal pads
4, Installation and usage tips (to avoid leakage)
The flange surface is clean without scratches or rust, with a roughness of Ra3.2~6.3 μ m
The gasket should be centered, not skewed or stretched, and it is strictly prohibited to stack multiple layers of gaskets
Tighten the bolts in a cross pattern in multiple stages, evenly pre tighten, and strictly prohibit unilateral force
Non metallic gaskets are disposable; It is recommended to replace the wrapping pad and metal pad after disassembly
High temperature condition: After heating up, tighten the bolts again to compensate for the thermal expansion gap
5, Common gasket marking examples
Wrapping pad: DN100 PN16 304+graphite inner and outer rings
Octagonal pad: R37 316L (compatible with RJ flange)
PTFE pad: DN80 PN10 PTFE
